The 2-(2-hydroxyphenyl)-2H-benzotriazoles represent a very important class of commercial UV-absorbers which have found wide-spread acceptance as stabilizers for protecting a host of organic substrates against the deleterious effects of exposure to actinic radiation.
With such a long period of commercial and technical interest in this class of compounds, there are a host of publications and patents describing this general class of compounds. Few of these references recite substitution of 2H-benzotriazoles with any group containing sulfur, let alone with a thioether moiety.
European Patent Application No. 323,853, pertaining to the stabilization of color photographic material, discloses generically 2H-benzotriazole compounds which may be substituted on the benzo ring, on the phenyl ring or on both rings by a host of possible substituents including inter alia alkylthio or arylthio moieties. Only 5-methyl-thio-2-(2-hydroxy-3-sec-butyl-5-tert-butylphenyl)-2H-benzotriazol e is specifically named. This reference defines the benzotriazoles very broadly without exemplification of compounds containing 5-alkylthio or 5-arylthio substitution, and it does not point out the beneficial stabilization properties obtained when an alkylthio or arylthio moiety is located on the 5-position of the benzo ring.
U.S. Pat. No. 3,766,205 describes 5-mercapto-2-(2-hydroxy-3,5-dimethyl-phenyl)-2H-benzotriazole and the ester prepared by the Michael addition of said mercaptan to ethyl acrylate. The instant compounds are structurally distinguished from the Michael adducts of this reference. The prior art Michael adducts are subject to thermal retro Michael cleavage to eliminate the acrylate group. Such compounds would be expected to have lower thermal stability than the instant compounds.
The instant compounds and compositions are distinguished from the compounds of the prior art. None of these references disclose that substitution of a 2H-benzotriazole compound in the 5-position of the benzo ring by an alkylthio, arylthio or aralkylthio moiety results in a significant increase in UV absorbance and also shifts the absorption maximum by about 20 nm toward longer wavelength relative to benzotriazoles without such 5-thio substitution. Such increased absorbance coupled with the red shift of the absorbance maximum toward higher wavelengths enhances the protection of substrates sensitive to longer wavelength ultraviolet light (near visible), such as coatings, plastics and fibers.